A Preliminary Studies on the Reproductive Biology of the Scomber australasicus in the Northeastern Waters off Taiwan

• Main Authors: Wei Liang Yu, 魏良佑
• Other Authors: Lee Kuo Tien
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/55041989602926761046

碩士 === 國立海洋大學 === 環境生物與漁業科學學系 === 91 === Mackerel is one of the most important catch in Taiwan’s northeast coastal fisheries, of which, jack mackerel (Scomber australasicus) makes up over fifty percent of the total catch. In recent years, there has been a gradual decline in its annual reproduction and catch rate. Vital bio-ecological information such as spawning period, spawning grounds, growing grounds, distribution, and migration that are necessary for resource management is lacking, however. This research is based on mackerel (Scomber australasicus) caught from mackerel/jack mackerel purse seiner, two-boat purse seiner, and Danish seiner in Taiwan’s northeast waters from February 2001 to December 2002. Body length, body weight, gonad weight, liver weight, and stomach content weight of the collected mackerel specimens were gathered to study their feeding, nutritional, and reproductive conditions. AVHRR’s sea surface temperature imageries were applied to analyze the distribution and migration characteristics in relation to environmental factors such as front index (FI) and monthly catch location. Our findings show the following: a)Based on the length frequencies of mackerel caught between February 2001 and December 2002, mackerel from northeastern Taiwan waters ranges from 20cm to 40cm. During the summer, fall and winter months of June to January, smaller mackerel with body length of 20-28 cm can be found in the fishing ground. b)The Gonosomatic Index (GSI) indicated that mackerel matures and spawns between January and May. In addition, results from the gonad histology indicated that the female mackerel reaches a high maturity rate between March and May, which implied that the spawning period reaches its peak during that time. c)The peak of the male mackerel’s Hepatosomatic Index (HSI) was between June and July, whereas the female mackerel’s HSI peaked in March and July. The Index of Stomach Fullness (ISF) showed that the male peaked in October and November, whereas the female peaked in March and April. The female ISF peak period correlates with its GSI peak period, suggesting that the female mackerel feeds profusely prior to spawning. d)The FI from satellite imageries and the mackerel’s CPUE distribution and concentration data showed that the spawning grounds for mackerel between March and May are in the Hua-pin Island, Mein-hwa Island, and Peng-chia Island to I-lan outer bay areas. The spawns are carried by Kuroshio countercurrent to the northeast waters where they nurse, but some are drifted by Kuroshio Current to the East China Sea continental bank. Between June and December, the matured mackerel migrates back to the northeast Taiwan waters where they feed.